The overall objective of this research is to elucidate the pathway of electron transfer and the mechanism of energy transducing proton translocation in the cytochrome bc1 complex of the mitochondrial respiratory chain. During the forth-coming project period experimentation will be focused on identifying the proton translocation reactions and the redox proteins involved in those reactions. The specific aims of the experimentation are to locate a ubiquinone and/or ubiquinol binding site, presumably on the iron-sulfur protein of the bc1 complex, from which protons are released coincident with electron transfer. Related studies will be conducted to test for a similar quinone/quinol binding site on cytochrome b. A second aim of the experimentation will be to test whether cytochrome b is a transmembranous, redox linked proton pump. These studies will be carried out with mitochondria and with two species of aerobic bacteria which offer unique advantages to answering aspects of these questions which are not as readily answered by experimentation with mitochondria. The methods to be used include purification of membranous respiratory chain complexes into phospholipid vesicles, and photoaffinity labeling.